In looking at power banks I see spec like,
“12000mAh” External Power Source Portable Power Bank w/ LED Flashlight
actual capacity 5200mAh / 1A+2A output
.
Why does a 12,000 mAh power bank have an actual capacity of 5200 mAh?
Jerry
The power bank is using a battery that has lower voltage than 5v and uses a boost converter to get the full 5v.
5200mAh at 5v is 10400mAh at 2.5v so if the battery inside the power bank is is about 2.2v then it would be 12000mAh
But that’s not counting inefficiency so it might be a 2.4v battery inside (two 1.2v nimhs in series)?
Inside a power bank are lithium cells that have a voltage of 3.7V. USB has a voltage of 5V. So if you take 12000mAh (at 3.7V) they convert to 8880mAh (at 5V). This calculation is without conversion losses. Good power banks have an efficiency of >90%.
So this was the theory. But still your numbers seem odd.
Thanks guys, I appreciate the help.
Jerry 